The invention relates to laser beam generation and, in particular, to the excitation of a laser gas by an electronic energy charge transfer derived from an excited donor gas.
A principal object of the invention is to provide a continuous-wave (CW), scalable, short wavelength (UV-visible) efficient gas laser. Electronic charge transfer from a noble gas donor to a lasing gas acceptor is employed to excite the laser gas. CW operation is achieved by continuously flowing the noble donor gas through an electical field before mixing it with a continuous supply of acceptor gas, the electrical field energizing the donor to a charge-transferable state.
The efficacy of electron charge transfers from noble gas donors to acceptor gases is an established fact and UV-visible lasers utilizing the present transfer mechanisms have been demonstrated. For example, a paper entitled "A Nitrogen Ion Laser Pumped by Charge Transfer" authored by C. B. Collins, A. V. Cunningham and M. Stockton has been published in Applied Physics Letters, Vol 25, number 6, page 344, Sept. 15, 1974. The charge transfer of this reference is from a donor gas, He.sub.2 .sup.+. Also, U.S. Pat. No. 3,970,964, July 20, 1976, N. Thomas Olson, Earl R. Ault and Mani L. Bhaumik, "High Power Argon/Nitrogen Transfer Laser" describes a laser exhibiting an output wavelength at 3577 A. Argon is the preferred donor gas although others are suggested. Transfer lasers such as these He/N and Ar/N examples, represent significant advances. For one reason, they provide laser beam sources in the UV-visible region and such sources have a number of important applications in fields of isotope separation, underwater communication, etc. Earlier work presented difficulties particularly involving a need for high pressures and a resulting low electron temperature which was unable to effectively excite the upper laser level of the gas in UV-visible lasers.
Although these prior transfer lasers are of considerable interest, it is to be noted that they both are pumped by pulsed E-beams or, in other words, they both are pulsed rather than CW lasers. Pulsed lasers, of course, are rather common and, for many applications, they are entirely acceptable. The continuous wave mode, however, considerably extends the use potential and provides some real advantages well recognized in the art. Further, the E-beam excitation or pumping of these pulsed lasers itself imposes limits on scalability or the potential for power increases. One limit, for example, is imposed by the so-called magnetic `pinching ` effect occuring at certain high E-beam levels. As will become apparent, the present CW laser is not so restricted. Instead, because of its mode of operation and its structural arrangement, scalability becomes relatively unlimited.